Mixing up php and html files

Right now I have 2 files, a php file and an html file and I want to make a form. In my html file I have the contents of the website as well as my form. In my php file (named contact.php) I am trying to process the inputs in php. Right now when I click submit, the html form brings me to my php file and doesn't echo the inputs. I know I could make take all the html and php into one php file and this would work, but is there any way to do it with what I have now.